See https://news.ycombinator.com/reply?id=21700802 and https://en.wikipedia.org/wiki/User:Guy_Macon/Wikipedia_has_C...
Letting the endowment grow by at least inflation is already covered in my essay:
"We should make spending transparent, publish a detailed account of what the money is being spent on and answer any reasonable questions asking for more details. We should limit spending increases to no more than inflation plus some percentage (adjusted for any increases in page views), build up our endowment, and structure the endowment so that the WMF cannot legally dip into the principal when times get bad."
"If we do these things now, in a few short years we could be in a position to do everything we are doing now, while living off of the endowment interest, and would have no need for further fundraising. Or we could keep fundraising, using the donations to do many new and useful things, knowing that whatever we do there is a guaranteed income stream from the endowment that will keep the servers running indefinitely."
They hold just under 135 million in assets, so they'd need 12 times what they currently hold. That's why living off interest wouldn't work. They'll need the telethon til they can make that equation work, or at least come closer.